This is possibly a silly question, but I'm psyching myself out at the thought of drilling into my new roo's bathroom walls..
I've searched the forums and found a few threads on where people discuss where they put the tp holder and towel holder, but not so much how to do it..
Do I have to look for studs or can you mount/drill anywhere?
If I put the tp holder on the back of the bathroom door can I drill anywhere on the door?
How far apart are the studs? (my stud finder isn't picking up on them too well..probably time for a new one).

I just used the screws that came with the TP holder and put it where I wanted. Others use velcro or double sided tape. I would not worry about hitting a stub in there, not using it as a handle... Hopefully.

I use a door hangar for the bath towels (goes over the top lip). A wet towel can be heavy. Have the hand towel on the wall mounted holder.

Yeah I have the over the door towel holder as well. I was thinking about using the towel holder they supplied somewhere near the kitchen and was wondering if the same rules apply with the wallboards being sufficient enough.

If your gonna use it in the kitchen for anything more than a dish towel I would shoot for mounting to a cabinet maybe. I mounted our napkin and paper towel holders to the side of the cabinets. They are solid wood on mine.

You can screw the TP holder to the inside of the lower sink cabinet door, or there is a hanging type that can be hung from the inside of the lower cabinet door.

We all do not want to 'mess up' the newness of what we just bought, but we all want to make some changes to fit our needs. Slowly make the changes, it is your camper. Just don't go so far as to void warranties and then want to 'come back' and have the Dealer 'fix it' back at no cost. All of the wall boards can be replaced if you 'go to far'.... also, hardware stores sell 'plugs' that can be put in the holes if they get wormed out too much and it will look natural. Make the changes you want. Start small and work your way up.